I am running a SBC DSL through a speedstream modem to a Dlink DI-604 4-port router. Every once-and-awhile the router will loose the internet. I've gone over the router multiple ties to make sure it's working fine, and I haven't found a thing wrong with it. What could be causing it to do this? It seems to be purely random at this point.

I would be interested in knowing how you have gotten your internet connection back in the past. What have you done to resolve this issue so far?

Such as: Do you reboot the computer and the internet connection comes back?

Normally restart both the modem and the router and it comes back. One of the 2 items is fouling itself, but I can't figure out which one.

Well, it's a bit of a shot in the dark here, but you could always try to update the firmware in the router by downloading the latest version from HERE.